Real-Time Monitoring and Prediction of Modes of Coherent Synoptic to Intraseasonal Tropical Variability

Abstract

A technique of near-real-time monitoring and prediction of various modes of coherent synoptic to intraseasonal zonally propagating tropical variability is developed. It involves Fourier filtering of a daily updated global dataset for the specific zonal wavenumbers and frequencies of each of the phenomena of interest. The filtered fields obtained for times before the end of the dataset may be used for monitoring, while the filtered fields obtained for times after the end point may be used as a forecast. Tests of the technique, using satellite-observed outgoing longwave radiation (OLR) data, reveal its skill for monitoring. For prediction, it demonstrates good skill for the Madden?Julian oscillation (MJO), and detectable skill for other convectively coupled equatorial modes, although the decaying amplitude of the predictions with time is a characteristic that users need to be aware of. The skill for the MJO OLR field appears to be equally as good as that obtained by the recent empirical MJO forecast methods developed by Waliser et al., and Lo and Hendon, with a useful forecast out to about 15?20 days. Unlike the previously developed methods, however, the current monitoring and prediction technique is extended to other defined modes of large-scale coherent zonally propagating tropical variability. These other modes are those that appear as equatorial wavelike oscillations in the OLR. For them, the skill shown by this empirical technique, although considerably less than that obtained for the MJO, is still deemed to be high enough for the technique to be sometimes useful, especially when compared to that of a medium-range global numerical weather prediction (NWP) model.